The present invention relates to objects fabricated of platinum and palladium which are provided with a hard and scratch-proof surface layer containing boron. The platinum can be alloyed with up to 25% by weight other noble and base metals and the palladium can be alloyed with up to 65% by weight of other noble metals and up to 15% by weight base metals. In a further aspect, the present invention also relates to a method of producing such fabricated objects.
Fabricated articles and objects consisting of platinum and platinum alloys play an increasingly greater role, particularly in the jewelry trade. Palladium alloys are also increasingly used for scientific technical purposes. Pure platinum and pure palladium are very soft and can not be brought up to very high hardness values even by adding other noble and base metals to form alloys thereof without losing other characteristic properties. In the case of rings or watch-cases, this deficiency results in the surfaces of such articles being easily scratched.
Hardness values of up to approximately 300 kp/mm.sup.2 can be achieved by adding e.g. iron, cobalt, boron or silicon in an alloying method using metallic fusion, at which time intermetallic phases develop which are important for attaining the hardness.
EP-OS 0,274,239 teaches scratch-proof platinum objects wherein elements such as aluminum, chromium, titanium or zirconium are allowed to diffuse into the surface of the object to form intermetallic compounds such as PtAl.sub.4, Pt.sub.3 Al or Pt.sub.2 Al.sub.3 in the surface layer. Boron is cited, among others; however, no examples or method parameters are indicated. The formation of intermetallic compounds does bring about an increase of hardness in the surface layer but has the disadvantage that a heterogeneous, multiphase structure is obtained with non-uniform properties. Moreover, relatively high concentrations of the metal diffusing into the surface layer are necessary in order to achieve the desired hardness effects. As a result thereof, such objects are not capable of being hallmarked in the jewelry trade.